Autonomic Nervous system

How to the SNS and ANS overlap in function?

*Maintaining homeostatic balance.* Most of the body's adaptations to changing internal and external conditions involve both skeletal muscles and visceral organs. For example, when skeletal muscles are working hard, they need more oxygen and glucose, so autonomic control mechanisms speed up heart rate and dilate airways to meet these needs and maintain homeostasis.

Anatomical differences in sympathetic and parasympathetic divisions

1.)Sites of origin 2.)Relative lengths of their fibers 3.)Location of their ganglia

Peripheral nervous system

A division of the nervous system consisting of all nerves that are not part of the brain or spinal cord

Autonomic nervous system

A subdivision of the peripheral nervous system. Controls involuntary activity of visceral muscles and internal organs and glands (*smooth and cardiac muscle tissue*) via the sympathetic and parasympathetic nervous systems.

Somatic nervous system

A subdivision of the peripheral nervous system. Enables voluntary actions to be undertaken due to its control of skeletal muscles (through somatic sensory and somatic motor nerves).

Efferent pathways of the somatic nervous system

A thick, heavily myelinated somatic motor fiber makes up each pathway from the CNS to the muscle. The motor neuron cell bodies are in the CNS, and their axons extend in spinal or cranial nerves all the way to the skeletal muscles they activate.

Efferent pathways of the autonomic nervous system

A two-neuron chain from the CNS to effector organs: 1.) The cell body of the first neuron, the preganglionic neuron, resides in the brain stem or spinal cord. Its axon, the preganglionic axon, synapses with the second motor neuron. 2.) The postganglionic neuron (sometimes called the ganglionic neuron) is the second motor neuron. Its cell body is in an autonomic ganglion outside the CNS. Its axon, the postganglionic axon, extends to the effector organ.

Neurotransmitters in the somatic nervous system

All somatic motor neurons release acetylcholine (ACh) at their synapses with skeletal muscle fibers. They are *always stimulatory/excitatory*

Neurotransmitters in the autonomic nervous system

Autonomic postganglionic fibers release two possible neurotransmitters to effectors. Norepinephrine (NE) is secreted by most sympathetic fibers and ACh is secreted by most parasympathetic fibers. *The effect can be either stimulatory or inhibitory*, depending on the types of receptors present at the synapses with different target organs.

Parasympathetic nervous system example

Best illustrated in a person who relaxes after a meal and reads a magazine. Blood pressure and heart rate are regulated at low normal levels, and the gastro-intestinal tract is actively digesting food. In the eyes, the pupils are constricted and the lenses are accommodated for close vision to improve the clarity of the close-up image.

Effectors of autonomic nervous system

Cardiac muscle, smooth muscle, and glands

Ganglia

Collections of nerve cell bodies in the peripheral nervous system. *They are also* sites of synapse and information transmission from preganglionic to postganglionic neurons.

The parasympathetic division is also called the

Craniosacral division; its preganglionic fibers spring from opposite ends of the CNS—the brain stem and the sacral region of the spinal cord; *Cranial and Sacral (S2-S4)*

The parasympathetic can be thought of as the ___ division

D division; digestion, defecation, diuresis (urination)

Sympathetic nervous system function examples

During any type of vigorous physical activity, the division also promotes other adjustments. 1.) It constricts visceral (and sometimes cutaneous) blood vessels, shunting blood to active skeletal muscles and the vigorously working heart. 2.) It dilates the bronchioles in the lungs, increasing air flow (and thus increasing oxygen delivery to body cells). 3.) It stimulates the liver to release more glucose into the blood to accommodate the increased energy needs of body cells. 4.) At the same time, the sympathetic division temporarily reduces nonessential activities, such as gastrointestinal tract motility (digestion). It is more important to give your muscles everything they need to get you out of danger.

A ___ exists between the divisions (sympathetic and parasympathetic), and both make continuous fine adjustments to ___.

Dynamic antagonism; maintain homeostasis

The sympathetic can be thought of as the ___ division

E division; exercise, excitement, emergency, embarrassment

Autonomic ganglia are also considered

Motor ganglia, containing the cell bodies of motor neurons

Sympathetic nervous system function

Often called the "fight-or-flight" system, which becomes evident when we are excited or find ourselves in emergency or threatening situations, such as being confronted and robbed late at night. A rapidly pounding heart; deep breathing; dry mouth; cold, sweaty skin; and dilated pupils are sure signs of sympathetic nervous system mobilization.

Effectors of the somatic nervous system

Skeletal muscles

Parasympathetic nervous system function

Sometimes called the "rest and digest" system, keeps body energy use as low as possible, even as it directs vital "housekeeping" activities like digesting food and eliminating feces and urine.

Sympathetic nervous system

The division of the autonomic nervous system that arouses the body and mobilizes its energy in stressful situations (*involuntary*)

Parasympathetic nervous system

The division of the autonomic nervous system that is in charge of maintenance at rest (i.e. digestion); calms the body, conserving its energy (*involuntary*)

Nature of parasympathetic fibers

The preganglionic axons extend from the CNS nearly all the way to the structures they innervate. The ganglia, or in this case *terminal ganglia* are *closer* to the actual target organs. There the axons synapse with short postganglionic neurons that will then synapse with effector cells in the immediate area.

The somatic and autonomic nervous systems differ in

Their effectors (muscles/glands controlled), efferent pathways + ganglia, and target organ responses to their neurotransmitters

Most spinal nerves (and many cranial nerves)

contain both somatic and autonomic nerve fibers

The somatic motor division

lacks ganglia entirely

Conduction in the ANS is ___ than in the SNS because ___.

slower; there is less myelination present.